The invention is based on a priority application EP08001689.2 which is hereby incorporated by reference.
The invention relates to a method for monitoring a passive optical network, PON, having a tree-like structure with a main line and at least two branches, to a monitoring unit connectable to a branch of a PON, and to a PON having a tree-like structure with a main line and at least two branches comprising monitoring units.
In order to improve the quality of service of optical networks, in particular passive optical networks (PONs) with a tree-like structure, continuous monitoring techniques detecting and localizing faults are of special interest, as they are expected to provide substantial cost savings to telecommunications companies operating these networks.
However, due to the large distances which are covered by the fiber links of a PON, a network operator usually only has access to the network from the main line, in particular from an optical line termination, OLT, which is located at a head end of the PON. For checking the functionality of the branches of the PON from the main line, it is known to dispose monitoring units in these branches which are usually arranged close to the location of the end users.
The downstream communication between the OLT and the monitoring units may be performed by the transmission of binary information including an identifier for a particular monitoring unit which may then execute a predefined function. In this respect, EP 1 037 417 B1 discloses a method for performing central control of an in-line element e.g. an optical amplifier or an optical switch in a tree-like network, wherein the OLT adds extra bits in predefined grants sent downstream to the in-line element. These extra bits comprise an identification of the in-line element and contain a locally predefined function for execution by the selected in-line element.
For performing downstream communication in the way described above, expensive equipment is required in the monitoring units, as the binary down-stream signal has to be processed in each of the monitoring units in order to determine which of the monitoring units is addressed by the OLT. For this purpose, a processing unit which is capable of processing binary data is required which has to Listen permanently to the downstream traffic, leading to a considerable energy consumption of the monitoring units.